xii. CORALLINE OOLITE. 299 



is varied with beds and large nodules of sandstone slightly cal- 

 careous, while, for a considerable space towards Littlemore, lie 

 widely-interrupted parts of the next rock above, viz. coralline 

 oolite. The oolite lies in separated patches on the same plane, which 

 were probably connected ; the intervals between them are occupied 

 by sand which may be supposed to have been left after the decom- 

 position of the oolite. The upper parts of the oolite are absent 

 for a large tract hereabout ; and it may be supposed that the large 

 waste of them was caused by long exposure to atmospheric agency 

 in very ancient times (pre-glacial or earlier). This process of surface 

 waste has affected a great part of the area of coralline oolite in 

 Oxfordshire, Berkshire, and Wilts, and seems to explain the patchy 

 and irregular distribution often observable in this rock ; though, 

 as far as relates to the purely oolitic and not shelly part of the 

 rock, the original circumstances of deposit must be taken into 

 account. 



CORALLINE OOLITE. 



A part of this rock is formed of considerable masses of coral 

 .mixed with many shells the ' Coral rag' of Smith ; other parts 

 contain large spherical or egg-shaped grains the ' Pisolite' of the 

 same author ; extreme total thickness 40 or 50 feet. Coral beds of 

 much continuity can hardly be quoted, yet the mixed mass of coral 

 and shells may justly be compared with some parts of the Bermuda 

 reefs, which are formed under the influence of currents in extended 

 sheets, while others grow up in vertical accretion. The upper 

 surface of the more oolitic part of the rock under the Kim- 

 meridge clay at Heddington is water-worn. The quarries at this 

 place have been used for extracting stone to build some colleges 

 in Oxford. It is found to be far from durable ; the best example 

 being in Wadham College, which had exceptional means of selecting 

 material from the best quarries. No other locality has furnished 

 much building-stone from this oolite, though at Wotton-Basset it 

 is largely excavated for walling and lime-burning. The lower and 

 more shelly parts of the rock are usually found near Oxford much 

 disintegrated by atmospheric action and rain currents, whereby 

 the corals and shells are separated and form a loose congeries of 

 remarkable aspect. The lowest beds are not thus broken up, but 

 remain solid and shelly, and make a sort of cap to the subjacent 



